The invention relates to wireless communication networks, and, more particularly, to handoff and site selection schemes in a wireless communication network.
Advanced third-generation (3G) and beyond wireless communication systems—such as the WCDMA High Speed Data Packet Access (HSDPA) system, Qualcomm's High Data Rate (HDR) system, or systems based on the CDMA2000 standard—are capable of supporting high-speed downlink packet services. See, e.g., 3GPP Technical Specification 25.308 version 5.2.0, “High Speed Downlink Packet Access (HSDPA): Overall description,” March, 2002; P. Bender et al., “CDMA/HDR: a bandwidth-efficient high-speed wireless data service for nomadic users,” IEEE Commun. Mag., pp. 70-77, July, 2000; 3GPP2 C.S0024 Version 3.0, CDMA2000 High Rate Packet Data Air Interface Specification, December, 2001. Such systems can take advantage of recent advances in opportunistic downlink scheduling algorithms, which exploit the asynchronous peaks of the fading channels of multiple mobile stations within a cell where a time-slotted downlink shared data channel is deployed. Unfortunately, the proposed scheduling algorithms have focused on the effect on individual cells, and little study has been devoted to multi-cell systems where inter-cell interference and asymmetric traffic arrival may be a major hindrance to higher resource utilization and better robustness.
Existing handoff and cell site selection schemes have mainly been developed for traditional multi-cell cellular systems, where each mobile station has a dedicated downlink channel from the base station. See, e.g., 3GPP Technical Report 25.950 v4.0.0, “UTRA High Speed Downlink Packet Access,” 3GPP, 2001; A. C. K. Soong, Ericsson, “Summary of the Cell Selection Ad Hoc Group,” TSC-C Working Group, 3GPP2/TSG-C30-20020311-020, 3GPP2 Cell Selection Ad Hoc Group, March, 2002; A. Gholmieh, P. Gaal, Qualcomm, “Cell Selection Discussion, QCOM Cell Selection Method,” TSG-C Working Group, 3GPP2/C30-20020311-009, 3GPP2 Cell Selection Ad Hoc Group, March, 2002; J. Li, Nortel Networks, “Update for Cell Switching Proposal,” TSG-C Working Group, 3GPP2/C30-20020311-015, 3GPP2 Cell Selection Ad Hoc Group, March, 2002; D. Knisely, S. Basudeban, Y. Yang, Lucent, “Requirements for Cell Switching in 1x-EVDV,” TSG-C Working Group, 3GPP2/C30-20020311-008, 3GPP2 Cell Selection Ad Hoc Group, March, 2002; Motorola, “Fast Cell Selection and Handovers in HSDPA,” TSG-RAN Working Group, R2-A010017, January, 2000. These prior art schemes typically consider only physical-layer channel quality and may potentially cause local congestion and high blocking rates in a system providing high-speed packet access.
It has recently been proposed that adding a centralized scheduler to a multi-cell system can be used to coordinate scheduling and load balancing. See S. Das et al., “Dynamic Load Balancing through Coordinated Scheduling in Packet Data Systems,” in Proc. IEEE INFOCOM, April, 2003. The central scheduler would determine the optimal base station-mobile station binding through periodic searching of a complete list of all the possible bindings. The list of static bindings would be sorted by radio distance (SINR) and the decision would be refined iteratively according to a threshold defined by the SINR based bindings. The dynamic binding across the system, together with independent scheduling within each cell, is referred to as “two-tier scheduling.”